As well known, NTSC color television systems adopted an interlaced scanning system to reduce the transmission bandwidth requirements. The interlaced scanning video displays half of each frame (called a field) every 1/60 second, followed by the other field 1/60 second later. Referring to FIG. 1, it illustrates the interlaced scanning video format with a top field and a bottom field of the prior art. The top field contains all the odd-numbered horizontal lines, and the bottom field contains all the even-numbered lines. However, the interlaced scanning manner has drawbacks of visual artifacts, including edge flicker, shimmering and diagonal jaggedness. Deinterlacing can overcome above problems to improve the appearance of the interlaced scanning video by converting the interlaced scanning video format into a progressive scanning format. Besides, many applications, such as PC displays, projection and high-definition television employ progressive-scan technology. To convert the interlaced scanning pictures to progressive scanning pictures, the missing lines of each field (for example, the even-numbered lines in the top field or the odd numbered lines in the bottom field) are generated from the interlaced scanning video signals.
One method for the interlaced-to-progressive conversion is a static technique that uses the same overall conversion regardless of the image sources or contents. This method uses the techniques of line replication, vertical filtering and field merging. Line replication repeats each horizontal line in a field to create a complete frame. Vertical filtering creates missing lines by filtering a number of nearby lines. Field merging takes lines from the previous field and inserts them into the current field to construct the frame. However, these approaches result in visual artifacts such as serrated edges for motion objects in the video frame.
To overcome these drawbacks, adaptive deinterlacing techniques are developed. Such adaptive deinterlacing techniques use motion analysis to select the optimum method for different parts of the image. Adaptive deinterlacing techniques first check both the current and one or more previous fields to determine the motion contents. In image sequences with little or no motion, missing lines take pixels values from the previous field. If there is a significant motion, an edge adaptive spatial interpolation method is used to construct the missing lines.
However, the above-mentioned approaches using adaptive interlacing techniques have complex computation procedure to determine the motion contents and interpolate the missing pixels values. U.S. Pat. No. 5,019,903 describes a technique which only considers how to interpolate the missing pixels without details to the motion detection circuit. U.S. Pat. No. 5,473,383 uses extra buffers to store the signals representative of the motion signals. U.S. Pat. No. 5,592,231 uses a median filter to select motion signal and applies five-edge interpolations. U.S. Pat. No. 5,532,751 uses two fields in the same frame to detect motion. U.S. Pat. No. 5,339,109 uses three-edge interpolation without order but does not consider the sharpness of the edges. However, the improper edge interpolation will blur the image.